Sunday, October 31, 2010

Trick or Treat†

It's time for another Accretionary Wedge. This month's theme is "Deskcrops," which I had intended to use as a showcase for the weird and wacky stuff that we geologists accumulate over the years. I've seen departmental collections where the strangest things were in there. "Pebbles and Mortar" from Hadrian's Wall; flesh, bone, and adiposere (fat) from a dead rhino; 1 mL of Deuterium (heavy water); and many more strange and beautiful things.

Seeing that it's Halloween (and also my Birthday), I thought it might be neat to go Trick-Or-Treating in the geobloggers to see what I get. When I was a kid, I would split my loot into different piles. From stuff I liked, to things, like "Bit-O-Honey" that weren't really very good. Fortunately for me, all the stuff I got was great - and roughly fits into categories related to the rock cycle.

This was my costume:

I'm going to give pride of place to my contribution: a few chunks of Trinitite: the glass made out of fused sand and rock and bits of equipment (casing, wire, etc) that formed in the explosion from the first atomic bomb.

It doesn't look like much - just some greenish, glassy stuff - several vesicles, and "blobs" of melted, spherical droplets. It has a little radioactivity above background. But I did notice some interesting bits. It does have parts that fluoresce in long and short-wave UV light:There are a few flecks of orangy things. The chunk of rock they're sitting on is also showing off some nice fluorescence. I blogged about this chunk last week.

Igneous Rocks

First off, we'll go with igneous rocks. These are rocks formed by the "freezing" of molten rock. These rocks may form deep below the surface as an "intrusive," or erupted onto the surface as an "extrusive" rock (often in a dramatic volcanic eruption).

Philip at Geology Blues provided some "Lavasicles." And tells a tale of finding neat rocks hiding within an existing collection. No need to traipse around the world, just capitalize on what's at hand. Kind of like MacGyver...

Jess at Magma Cum Laude (she's probably still unpacking at her new blog-home) tricks us with an interesting scorch pattern on some pumice from the Sufriere Hills.

Ian from Hypo-theses, continues to blog about a rock each day. Quite a challenge. You know the post is going to be interesting when the exposition begins with a story about sitting around a bedouin campfire on the edge of the Sahara. We're treated to many photos of some kind of long-named, Norwegian pegmatite. Check out those phenocrysts!

Lockwood's blog, Outside the Interzone, gave us a neat hunk of pillow basalt. It includes the classic field photo (hammer for scale) to show its provenance. Also, not the only blog to photograph the rock with a cat for scale - there might be a theme here...

Sedimentary Rocks

Sedimentary rocks are either "clastic," which are made of broken fragments of pre-existing material compacted, cemented, and turned to stone. Or, they are "non-clastic" - I've never been a fan of classifying something by what it's not - so I prefer the term "chemical" for the other group of sedimentary rocks that are formed by precipitation out of solution.

Anne, over at Highly Allocthonous shows off some nifty cubes of rock she uses to teach about porosity and permeability. Incidentally, my house lies about 20 feet above the Eau Claire Formation in the stratigraphic sense. There's a slice of the Wonewoc and some unlithified sand/gravel outwash between us, but some of my drinking water comes from this aquifer. Many of our local springs form as a result of the interbedded shales that form local aquicludes (even perched water tables in the hills nearby).

Silver Fox, who is still Looking for Detachment, shows off a very Halloween-y hunk of dolomite breccia that looks like a Jack-O-Lantern. These kinds of rocks show that the distinction of "clastic" or "chemical" are not always useful. The big pieces of gray dolomite are clasts, but the whole thing is made of and cemented by the precipitation of minerals from solution.

Having been properly tricked, David at History of Geology provenance, shows off some lovely fossils from the eponymous "Dolomites." Incidentally, carbonate rocks are relatively susceptible to chemical weathering, but often resistant to physical weathering - especially in arid regions where they slowly weather into sharp little points and edges, that give rise to the term "tear-pants" topography. Those of you who have sat on these rocks have probably noticed how quickly this texture can slice open clothing, boots, and hands.

Metamorphic Rocks

A metamorphic rock is what happens to rock subjected to increased heat and/or pressures. These produce new textures and minerals as the rock deforms in response to these changes.

The Musings of a Life-long Scholar shows off a "deskcrop" that doesn't take up much space - a backscatter electron image of a monzonite grain. Photographs often contain a lot of data, and they take up much less space than the actual material.

Misc

Then there were some treats that didn't fit into a nice category. Like the multi-treat packs, they had a little bit of everything, or their post had some other geologically related theme.

Callan Bently and his Mountain Beltway, also unpacking into a shiny new home, shows off a bunch of samples. Does a vodcast count for a blog carnival? Seems kind of "fancy" for this show since everything else looks monodimensional by comparison. Kind of like being the following act after the talking pig at the county fair.

Helena Heliotrope from Liberty, Equality, and Geology shows off a spikey dogtooth spar and a hunk of orpiment. Orpiment is a pretty (if toxic) mineral with a chemical formula that's easy to remember As2S3. Just omit the subscripts. This works even better for Realgar.

Julia over at Stages of Succession shows off some "Labcrops" of biological specimens, including multicolored mammalian crania, critters in jars, and a few colorful remarks. I'm rather partial to the red maxillae and yellow frontals on the skulls.

John - from Karmasotra - shows off some clamshells. I believe they're all Mercenaria sp., showing various growth and bioerosion development stages. Plus a creepy comment about preserving beauty through death. What was that quote about "leaving a beautiful corpse..."?

Finally, one more trick: Ron Schott's Geology Home Companion, blogfather to many, and inspriation for this theme said he was working on a post. I'll link to it when it appears.

†The "tricked" blogs are all there, you just have to figure out how to see them... (hint: try selecting text).

UPDATE: Ann,who muses on geology and other things, has a post. It got lost in the shuffle and I wasn't able to find a link to the post until today. She writes a few musings about a piece of amber. As you may know, amber is the fossilized sap of trees. It has the interesting property of being slightly less dense than salt water, so sometimes chunks of amber erode out of the rock where they are preserved and wash up somewhere down the shore.

If you don't have a blog, but still want to participate - send an email to me (find it via the profile page). Include your name, a brief description, plus a photo (keep the file size reasonable, please). I'll add it to the mix.

Here's a preview:Many geologists have access to a rock saw now and then. The desire to cut rocks into useful/interesting shapes can have quite a pull. I have no idea where the rock came from (save for the UW Geology Museum Giftshop, or exactly what it is - it's mass is 776.9 g. An estimate for volume put it at 283.1 cm3, which gives a specific gravity of about 2.74. It scratches glass, but not quartz.

I think it has some quartz mixed in, but I'm not sure about the green stuff. It kind of matches some of the descriptions of Scapolite group minerals, but the color seems a little weird a few flecks do fluoresce a pale yellow-white. It's got a generally metamorphic vibe/fabric, which is probably why it's causing me trouble. And yes, "vibe" should be a diagnostic category for rocks and minerals - we can put that into the next edition of Hurlbut & Klein.

Monday, October 18, 2010

Today they "upgraded" our faculty email service. Which is an "upgrade" in the sense that the online storage space has exceeded 109 bytes. We were limited to 18MB before - a serious limitation nowadays, what with photos, video and all that. Heck, even text files and spreadsheets cut heavily into that space.

But, it's also "upgraded" in the sense that half of the faculty can't connect to things yet, it uses an unnecessarily complex web interface, and the functionality of all items uses a new idiom.

I'm going back to my Apple Mail program - at least I know how it works and where all my stuff is...

Oh, and check this out. Because we could all use some perspective on a Monday morning.

Wednesday, October 13, 2010

I did a test run of an eruption simulation I have planned for later in the week. It worked out pretty good. I threw a little video together to let you see what's going on. I'll have a more detailed post probably this weekend.

Tuesday, October 12, 2010

My "Pinhole Camera" post seems to be one of the more popular items on this blog. This morning, I tried something a little different. I placed a sheet of aluminum foil over a C-mount adapter, then poked a tiny hole in the middle of the foil. This turned the camera into a (rather expensive) pinhole camera. No lens required! Here's my old 10D with the setup:

After a little trial and error, I found that an exposure of about 13 seconds at ISO 800 produced a reasonable exposure.

You can see that the super-tiny aperture allowed for all the dust particles on the sensor to show up as dark gray blobs. It's been a while since I've cleaned the sensor (it's an old model that doesn't come with the auto-cleaning option). Also, the image is a little soft - if I had made the hole a little smaller, more round, and sanded the edges smooth it would have come out much sharper. But as a proof of concept, it worked wonderfully.

Monday, October 11, 2010

I came across a brief article on Wired.com with some pictures of Mars. The article describes the deepest valley in the solar system: the Melas Chasma on Mars. At some 5.6 miles, it's quite a bit deeper than anything we see here on Earth.

The 3D rendered image they showed (high-res image linked here), showed some landforms that looked remarkably similar to unconfined, subaqueous debris flows that we can see here on earth. Basically, a turbidity current - which is a gravity-driven cloud of debris and fluid (some good videos of modeled versions here). One of the remarkable things about the Mars image is how clearly the leading "toe" of these debris flows stands out (arrows point to several of them - along with a nicely developed fault scarp and hummocky block of wasting cliffside).

I'm not sure how the mechanics of these things work on mars, but without a thick atmosphere to help "cushion" the flow and allow it to travel long distances, I wonder if it's Mars' reduced gravity that helps these things travel so far.

Friday, October 08, 2010

This has been a very wet summer for western Wisconsin. I was down in one of the local creeks, and noticed that there were many new bedforms in the sand on the creekbed. I saw that the sand bars at the mouth of the river were about ten inches above the water in the creek.

Our heavy summer rain helped dump a whole heap of sand into this little tributary stream. It flowed down to the big river, which was also swollen with extra rain. So the "base level" of the stream was higher during the summer. Now that the extra water has flowed away, the river level - and thus stream level - is lower. The "base level" of this little tributary stream has dropped. And as such, it will tend to carry sediment away towards base level. Ultimately, all rivers' "base level" ends at the sea. Although even this is a little misleading, since there are huge undersea canyons that act as weird fluvial systems in their own right. Check out Clastic Detritus sometime, as he often talks about submarine canyons.

I just think I'll share some photos I took while I was there. Consider it a study of the intersection between the landscape, fluvial geomorphology, and art...

Tuesday, October 05, 2010

So, the semester is in full swing here at our fair University. I feel like I'm messing with the throttle because there are so many things I could be working on. Instead, I'm pausing between lectures to write a little blog update. I guess you could say the helm looks like this:

Judging by the spike in my visitor counts, Brian Romans' post of my braided river image has gone up.

For those of you that are new, welcome. Feel free to poke around. In other news, here's a picture for your entertainment:

Those of us that study the variety of processes that occur at or near Earth's surface, we sometimes have to account for the fact that living organisms often call this thin veneer of fragmented rock, organic debris, air, and water home. As they go about their lives, they often churn up these layers of meticulously deposited material. When viewed from the perspective of a geologist, we call it "bioturbation." When viewed from the perspective of a groundskeeper, it's called a "varmint." Technically speaking, it was probably a ground squirrel or a mole, not a gopher 'round these parts.

"Well, here we are! Pismo Beach and all the clams we can eat!"

"Hey, wait a minute! Since when is Pismo Beach inside a cave?"

I arrived at school one Monday morning to find this lovely tunnel lying exposed in the newly graded front "yard" of our newly renovated science building. I took a few pictures - the whole plot was smoothed over and seeded by the grounds crew before I could find a toy Bugs Bunny and Daffy Duck to place in the photo...